table: fix nexthop path attribute updating for normal BGP
table: fix nexthop path attribute updating for normal BGP

Paths whose route family are other than ipv4 have nexthop information in
a mp_reach_nlri path attribute instead of a nexthop path attribute.

Signed-off-by: ISHIDA Wataru <15703620d0b11e835ab4f34ebf88f2f40cce783e@lab.ntt.co.jp>

ishidawataru/gobgp,j-kato/gobgp,tamihiro/gobgp,tamihiro/gobgp,ramrunner/gobgp,osrg/gobgp,Dipsingh/gobgp,h-naoto/gobgp,a16/gobgp,a16/gobgp,a16/gobgp,a16/gobgp,osrg/gobgp,osrg/gobgp,Dipsingh/gobgp,ramrunner/gobgp,postfix/gobgp,tamihiro/gobgp,YujiOshima/gobgp,fujita/gobgp,h-naoto/gobgp,a16/gobgp,h-naoto/gobgp,postfix/gobgp,fujita/gobgp,ishidawataru/gobgp,fujita/gobgp,fujita/gobgp,a16/gobgp,Dipsingh/gobgp,osrg/gobgp,YujiOshima/gobgp,postfix/gobgp,tamihiro/gobgp,j-kato/gobgp,a16/gobgp,ishidawataru/gobgp,YujiOshima/gobgp,j-kato/gobgp,ramrunner/gobgp